1. Field of the Invention
The present invention relates to a nonlinear all-optical spatial light switch capable of operating at speeds in excess of 100 GHz, and, more particularly, to a switch in which the nonlinear medium includes a conjugated organic material in the form of a waveguide. The switch is controlled by amplitude (time domain) or frequency (frequency domain) modulation of a controlling light beam. The present invention can function as a spatial light switch or as an optical modulator or optical amplifier.
2. Description of the Prior Art
Increased use of optical fibres as a transmission medium in communication networks has resulted in improved communication bandwidths and reduced interference when compared with electronic communication systems.
It has been shown that optical fibres have the capability to transmit data rates.about.1 THz as described in the article `Experimental Observations of picosecond pulse narrowing, and solitons in optical fibres` by L. F. Mollenauer et Al. appearing in Physical Review Letters Vol. 45 No. 1, 1980 at pp. 1095-1097.
In order to implement a communication system capable of operating at such data rates it is necessary to have components such as switches and multiplexers/demultiplexers able to operate at similar speeds. It is also clearly preferable to have devices able to operate directly on the light signals themselves, without conversion to another communication medium. Electronic circuits cannot presently operate at 1 THz rates.
Current optical switching devices make use of the fact that at high electric field intensities the polarisation P of certain media is a nonlinear function of the electric field and can be expanded in powers of the electric field E. ##EQU1##
Electro-optic switches currently use materials in which X.sup.(2) is not zero and therefore exhibit the Pockels effect whereby an applied electric field alters the refractive index experienced by light propagating through the material. Examples are Gallium Arsenide and Lithium Niobate based devices. Such devices rely on electronic control of light and are limited in practice to speeds below about 10 GHz. They are also expensive to fabricate compared to the present invention.
Devices utilising the third order nonlinear effect (X.sup.(3) &gt;0) can directly control light with light via the optical Kerr effect. They rely on the fact that in an optical Kerr medium a light beam can locally alter the refractive index of the medium and influence other light beams. In particular the refractive index of the medium is goverened by EQU n=n.sub.0 =n.sub.2 I
where I is the local light intensity and n.sub.2 and n.sub.0 are constants. The constant n.sub.2 is related to X.sup.(3) in SI units by EQU X.sup.(3) =n.sub.0 .epsilon..sub.0 cn.sub.2
Devices utilising free carrier and exitonic third order nonlinear effects in semiconductors are slow compared to the present invention. There is also the problem that the medium as utilised in such devices is absorptive to light at wavelengths where the device operates.
There remains the need for an optical switch capable of routing light signals in an optical fibre communication system at rates approaching 1 THz, which can also form the switch components in multiplexers/demultiplexers, and can be controlled optically.